Generally, an electric apparatus includes a power source device for supplying an appropriate voltage to such things as an integrated circuit, a sensor, or a driver circuit. A switching regulator or a linear regulator can be included in examples of such a power source device. In recent years, power source devices have been increasingly applied to battery-powered mobile devices, and thus, it is increasingly desired that these power source devices achieve both low current consumption and high speed response.
For example, a method to keep an output voltage of the power source device constant is known. In this method, an operational current providing to an amplifier in the power source device is increased when the output voltage decreases. However, when a difference between a threshold value for determining an abnormal voltage and a normal voltage is set to be small, there may be a case where the additional current continues to erroneously flow into the amplifier, which increases current consumption. On the other hand, when the voltage difference is set to be large, the current in the amplifier does not increase if the output voltage does not significantly deviate from the normal voltage, which hinders high speed response. Furthermore, there is a problem of how to increase the current in the amplifier in response to the decrease of the output voltage. As described above, the achievement of low current consumption and the achievement of high speed response are in conflict. Therefore, it is desired to obtain a method for achieving both the low current consumption and the high speed response.